James announced the news herself via Twitter on 8 October, following a three-month selection process by producers. Marcel is best known for her work on the hyped-but-swiftly-cancelled science fiction TV series Terra Nova, and has also penned Saving Mr Banks, a forthcoming film about Walt Disney's 20-year battle to bring Mary Poppins to cinemas. Starring Tom Hanks, Emma Thompson and Colin Farrell, Banks began filming last month.

The film version of Fifty Shades of Grey is being overseen by the producers of the Oscar-winning drama The Social Network, Michael De Luca and Dana Brunetti. Universal optioned the bestselling novel for $5m in March.

"Kelly's work demonstrates her flawless structural technique and passionate commitment to emotion, humour and depth of character, which is particularly visible in the celebrated screenplay for the upcoming Saving Mr Banks," De Luca said. Brunetti added: "We were all taken with the depth and passion of Kelly's engagement with the characters and world EL James has created, and we knew she was the right person to augment our Fifty Shades family."

However, the news of Marcel's appointment went down less well with the novelist and screenwriter Bret Easton Ellis, who had been energetically touting himself for the job until being told in August that he was not being considered. "Kelly Marcel: the creator of (gulp) Terra Nova and a Mary Poppins biopic has been blessed by EL James and no one can stop her," he wrote on Twitter. "Dear God." A separate tweet read: "Kelly Marcel?!? KELLY MARCEL?!? Kelly Marcel is WRITING the script for Fifty Shades of Grey?!? THIS is the movie they want to make? ARGH."

James's novel, about a rich businessman who recruits a young woman to be his well-remunerated sex slave, has sold over 40m copies worldwide. There has been furious speculation over who might play kinky business magnate Christian Grey and his paramour Anastasia Steel in the film, with Ryan Gosling and Mila Kunis the current favourites with bookmakers. Easton Ellis, meanwhile, has touted his own protege, the former porn star James Deen, for the role of Christian.